What are the specific requirements for Business Trip visa to China

I was opportuned to go to the Chinese embassy in Abuja but it was not funny. Based on the requirement on the website which was supplied I was still ask to provide another document which would be posted from the china its an authorised letter confirming my invitation letter from local affairs office. I guess inability to have access to an official in the embassy office is really bad. The place is being manned by security guys only who will check your documents and ask you questions which is not official.

The official should help more to ease travellers nightmares.